From Lewis Acid to Lewis Base by La-to-Y Substitution in α-YBO: Local Structure Modification Induced Lewis Basicity.

Different from the common perspective of average structure, we propose that the locally elongated metal-oxygen bonds induced by La-to-Y substitution to a Lewis acid α-YBO generate medium-strength basic sites. Experimentally, NH- and CO-TPD experiments prove that the La doping of α-YLaBO (0 ≤ ≤ 0.24) results in the emergence of new medium-strength basic sites and the increasing La concentration modifies the number, not the strength, of the acidic and basic sites. The catalytic IPA conversion exhibits a reversal of the product selectivity, i.e., from 93% of propylene for α-YBO to ∼90% of acetone for α-YLaBO, which means the La doping gradually turns the solid from a Lewis acid to a Lewis base. Besides, α-YBO ( = Ce, Eu, Gd, Tm) compounds were prepared to consolidate the above conjecture, where the acetone selectivity exhibits a linear dependence on the ionic radius (or electronegativity). This work suggests that the substitution-induced local structure change deserves more attention.